The present invent ion relates to a method for vulcanizing a tire and an apparatus used therefor.
Hitherto, the apparatus shown in FIG. 4 has been employed as an apparatus for vulcanizing a tire of a vehicle. In this case, a tire b is placed inside a mold a, the mold a is chased, and a bladder c is inflated by providing a shaping internal pressure, so that the shape of the tire b becomes to the inside shape of the mold and the tire is placed therealong. Then, steam as a heating medium is blown and supplied, in a nearly horizontal direction, into the tire internal space f to heat and pressurize the tire b. The steam is blown from a supply opening e which is arranged at a lower part of a center portion of the vulcanizing apparatus and communicates with a supply passage d. When the tire b is heated to a predetermined temperature or after a predetermined time period, the supply of steam is stopped and thereafter combustion gas, gaseous nitrogen, or the like as a pressurizing medium, the pressure of which is the same as or more than that of the stream, is supplied, in a nearly horizontal direction, into the tire internal space from the supply opening e. By virtue of the gas, the tire b is kept at a predetermined temperature during remaining time period for heating till tire vulcanization is finished.
In another case of the latest apparatus, it employs a structure wherein heating medium and pressurizing medium are supplied respectively through separated supply openings into the tire internal space.
In the above-mentioned prior art apparatus, pressurizing gas having a relatively low temperature compared with the steam is blown, in a horizontal direction, toward the lower portion of the tire from a supply opening arranged low relative to the tire b, from which the steam is also blown. Accordingly, a part to which the gas flow is directed (i.e. the lower bead g) is cooled and its temperature is lowered. Further, in a condition wherein the pressurizing gas inflow ceases due to an increase of the internal pressure and accordingly internal flow of the, pressurizing gas ceases, the gas tends to gather in the lower portion h of the internal space f of the tire b because the specific gravity of gas is relatively larger than that of steam. Accordingly, the temperature of a lower sidewall i and a lower bead g in contact with the pressurizing; gas of the lower temperature is lowered. On the other hand, steam tends to gather in an upper portion j of the internal space f of the tire b and the temperature of the steam rises by adiabatic compression, although it only lasts a short time, because of the gas introduced at a higher pressure though the temperature thereof is low. This causes temperature of an upper sidewall k and an upper bead l to rise.
Thus, in the tire internal space f, a layer mainly comprising steam in the upper portion j and another layer mainly comprising gas appears in the lower portion h. Accordingly, the temperature of the inside of the tire b changes as shown in FIG. 2. That is, after the gas is supplied, the temperature at the upper bead l tends to rise as represented by a virtual line 27, and the temperature at the lower bead g tends to fall as represented by a virtual line 28. Consequently, there occurs a large temperature difference (for example, 13.degree. C.) between the upper bead l and the lower bead g.
Once the above-mentioned large temperature difference occurs, it does not completely disappear till vulcanization is finished. For this reason, degree of vulcanization at the upper and lower sidewall differs from each other, and this is undesirable in respect of tire quality. In addition, since the necessary cure time is decided according to the, lower port ions of the tire where the speed of temperature rise is most retarded, the vulcanizing operation of longer duration has to be conducted and this is another undesirable problem also in respect of the productivity and energy saving.
The apparat us employing a structure wherein supply openings for heating medium and pressurizing medium are separately arranged has a drawback that the apparatus becomes complicated because the supply of mediums for valucanization is separated.
In consideration of the above-mentioned drawbacks of the conventional apparatus, an object of the present invention is to provide a method for vulcanizing a tire and an apparatus used therefor wherein a temperature difference is hard to occur inside the tire during vulcanization, uniform vulcanization can be carried out, and the structure of the whole apparatus is not complicated.